The study evaluates the effect of GSK2256294 exposure at steady state on pulmonary artery systolic pressure (PASP) in healthy volunteers, under hypoxic conditions, after 7 days of dosing. It is single centre, double blind, randomized, placebo-controlled study to be conducted in approximately 30 healthy volunteers. Subjects will be screened no more than 30 days. Subject will be admitted in clinical unit on Day -1. Subject will be dosed for 7 days in unit in morning on all days except for dosing on Days 3 -6. Dosing on Days 3 -6 will occur at home. Subjects will return to the unit on the evening of Day 6 and remain there until Day 8. Subjects will undergo echocardiography under normoxic and hypoxic on Day 1 pre-dose and on Day 7 post-dose. Subject will be followed up for 28- 32 days after discharge. The maximum estimated time that a subject will be enrolled in the study is 62 days from the screening visit to follow up.